Human bone marrow allograft recipients: production of, and responsiveness to, interleukin 2.

The production and utilization of interleukin 2 (IL 2) by peripheral blood mononuclear cells (PBMC) from 14 bone marrow allograft recipients was examined. PBMC from all patients were impaired in their ability to produce IL 2 when stimulated by phytohemagglutinin (PHA). On the average, the IL 2 activity produced by patients' PBMC was 8% of that from normal donors' PBMC. To examine the basis for this impaired T cell function in marrow recipients, the ability of a resting T lymphocyte population isolated from PBMC to respond to PHA and exogenously supplied IL 2 was analyzed. The proliferative response of resting T cells to PHA and IL 2, although low at early times post-transplant, reached near normal levels by 8 mo. Only two of 11 patients had normal numbers of precursor T cells that could respond. For all other patients the average number of precursor T cells was 10-fold lower than the average determined for normal donors. The impaired production of IL 2 by patients' PBMC may be due to this low precursor frequency. For some patients the rate and/or extent of clonal expansion of activated T cells appears to be greater than that of normal donors. The data suggest that the therapeutic application of IL 2 to such patients is unlikely to be successful in overcoming defects of T cell function before 8 mo post-marrow transplant.